总结：
主要包括几个重要的结构体、并发控制、以及ioctl的实现。在驱动的设计过程主要涉及3个重要的结构体。struct file_operations,struct inode,struct file.
struct file_operations主要是涉及一些文件操作的函数，其本质上就是一个函数指针的集合，包含了文件操作的各种函数声明，可能与应用程序设计中的相应函数只在参数上存在一定的差别。但是在2.6.36版本以后，其中的内容发生了较大的变化，主要设计了ioctl的相关操作。
struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
/*新添加的函数，同时去掉了ioctl的函数，同时返回值也发生了变化*/
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, int datasync);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
int (*setlease)(struct file *, long, struct file_lock **);
long (*fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
};
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
是最近添加进来的函数，为了实现原来的ioctl函数，同时参数以及返回值都发生了较大的变化，这也是为什么在2.6.36版本以后的内核中使用ioctl函数会报错的原因。unlocked_ioctl函数通常用来实现原来的ioctl函数，而compat_ioctl函数则用来实现一些兼容版本的ioctl问题。返回值由原来的int变为long型，也是需要注意的。在ioctl中，第一个参数是struct inode,2.6.36以后的版本将不能直接访问到inode参数，只能间接的访问，具体的访问方法后面在总结。
在驱动实现过程中主要包括对各个需要实现函数的赋值，但是open函数不能赋值与否，都会默认打开，如果不赋值，则默认该设备一直打开。其他的函数不赋值，即表示不实现该方法。常用的复制方法如下：
/*添加该模块的基本文件操作支持*/
static const struct file_operations mem_fops =
{
/*结尾不是分号，注意其中的差别*/
.owner = THIS_MODULE,
.llseek = mem_llseek,
.read = mem_read,
.write = mem_write,
.open = mem_open,
.release = mem_release,
/*添加新的操作支持*/
.unlocked_ioctl = mem_ioctl,
};
需要注意的是后面不再是分号，而是逗号。其中的mem_read、mem_write等是函数的具体实现过程。.owner表示该结构体属于那个，当然就是THIS_MODULE,表示这个模块。
struct inode表示的是一个文件的索引，该结构是每一个具体的物理文件（保存在存储器中的实体文件）的索引，一个文件对应一个唯一的struct inode，其中表明了文件的大小，文件的类型，文件的时间等参数，结构体中每一个参数都能表示某一个文件的特性，通过inode就能表示文件的所有信息。
struct inode {
/* RCU path lookup touches following: */
umode_t i_mode;
/*使用者的id*/
uid_t i_uid;
/*使用者的组的id*/
gid_t i_gid;
const struct inode_operations *i_op;
struct super_block *i_sb;
spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */
unsigned int i_flags;
struct mutex i_mutex;
/*状态标志*/
unsigned long i_state;
unsigned long dirtied_when; /* jiffies of first dirtying */
struct hlist_node i_hash;
struct list_head i_wb_list; /* backing dev IO list */
struct list_head i_lru; /* inode LRU list */
struct list_head i_sb_list;
union {
struct list_head i_dentry;
struct rcu_head i_rcu;
};
unsigned long i_ino;
/*引用次数，当这个数为0时，release函数才能完成*/
atomic_t i_count;
unsigned int i_nlink;
/*设备文件的设备号*/
dev_t i_rdev;
unsigned int i_blkbits;
u64 i_version;
/*文件偏移量*/
loff_t i_size;
#ifdef __NEED_I_SIZE_ORDERED
seqcount_t i_size_seqcount;
#endif
/*文件的时间参数，包括三种时间*/
struct timespec i_atime;
struct timespec i_mtime;
struct timespec i_ctime;
blkcnt_t i_blocks;
unsigned short i_bytes;
struct rw_semaphore i_alloc_sem;
const struct file_operations *i_fop; /* former ->i_op->default_file_ops */
struct file_lock *i_flock;
/*文件的备份地址空间*/
struct address_space *i_mapping;
/*设备地址空间*/
struct address_space i_data;
#ifdef CONFIG_QUOTA
struct dquot *i_dquot[MAXQUOTAS];
#endif
struct list_head i_devices;
/*说明了三种不同的驱动类型*/
union {
struct pipe_inode_info *i_pipe;
struct block_device *i_bdev;
struct cdev *i_cdev;
};
__u32 i_generation;
#ifdef CONFIG_FSNOTIFY
__u32 i_fsnotify_mask; /* all events this inode cares about */
struct hlist_head i_fsnotify_marks;
#endif
#ifdef CONFIG_IMA
/* protected by i_lock */
unsigned int i_readcount; /* struct files open RO */
#endif
/*写者使用次数*/
atomic_t i_writecount;
#ifdef CONFIG_SECURITY
void *i_security;
#endif
#ifdef CONFIG_FS_POSIX_ACL
struct posix_acl *i_acl;
struct posix_acl *i_default_acl;
#endif
void *i_private; /* fs or device private pointer */
};
驱动程序设计过程中通常采用i_rdev判断设备文件的设备号。
struct file是指文件对象，表示进程中打开的文件，一个物理文件只有一个inode,但是可以被打开很多次，因此可以存在很多struct file结构体。
struct file {
/*
* fu_list becomes invalid after file_free is called and queued via
* fu_rcuhead for RCU freeing
*/
union {
struct list_head fu_list;
struct rcu_head fu_rcuhead;
} f_u;
/*文件的路径*/
struct path f_path;
#define f_dentry f_path.dentry
#define f_vfsmnt f_path.mnt
/*该文件支持的操作集合*/
const struct file_operations *f_op;
spinlock_t f_lock; /* f_ep_links, f_flags, no IRQ */
#ifdef CONFIG_SMP
int f_sb_list_cpu;
#endif
/*文件对象的使用次数*/
atomic_long_t f_count;
unsigned int f_flags;
fmode_t f_mode;
loff_t f_pos;
struct fown_struct f_owner;
const struct cred *f_cred;
struct file_ra_state f_ra;
u64 f_version;
#ifdef CONFIG_SECURITY
void *f_security;
#endif
/* needed for tty driver, and maybe others */
/*通常用来指向具体的数据或者设备文件，实现操作*/
void *private_data;
#ifdef CONFIG_EPOLL
/* Used by fs/eventpoll.c to link all the hooks to this file */
struct list_head f_ep_links;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
unsigned long f_mnt_write_state;
#endif
};
访问inode主要是通过这两个机构体之间的管理型。
struct path {
struct vfsmount *mnt;
struct dentry *dentry;
};
struct dentry {
/* RCU lookup touched fields */
unsigned int d_flags; /* protected by d_lock */
seqcount_t d_seq; /* per dentry seqlock */
struct hlist_bl_node d_hash; /* lookup hash list */
struct dentry *d_parent; /* parent directory */
struct qstr d_name;
struct inode *d_inode; /* Where the name belongs to - NULL is
* negative */
unsigned char d_iname[DNAME_INLINE_LEN]; /* small names */
/* Ref lookup also touches following */
unsigned int d_count; /* protected by d_lock */
spinlock_t d_lock; /* per dentry lock */
const struct dentry_operations *d_op;
struct super_block *d_sb; /* The root of the dentry tree */
unsigned long d_time; /* used by d_revalidate */
void *d_fsdata; /* fs-specific data */
struct list_head d_lru; /* LRU list */
/*
* d_child and d_rcu can share memory
*/
union {
struct list_head d_child; /* child of parent list */
struct rcu_head d_rcu;
} d_u;
struct list_head d_subdirs; /* our children */
struct list_head d_alias; /* inode alias list */
};
其中的可以通过struct file间接的访问物理文件的struct inode,具体的实现是filp->f_path.entry->d_inode,这个过程也就实现了将inode和file结构体之间的联系。
上面的几个主要的结构体是驱动实现过程中最重要的几个。具体的意义还要联系起来分析。